The broad objectives of this research program are the acquisition of a better understanding of the detailed enzymatic mechanisms involved in the transformations of steriod hormones in microbial and mammalian systems. The principal reactions to be studied are: (1) Steroid oxidations and reductions by nicotinamide adenine nucleotide-linked hydroxysteroid dehydrogenases; (2) the delta 5-3-ketosteroid isomerase reaction which plays a critical role in the biosynthesis of all steroid hormones. Specific attention will be accorded to: 1. The basic mechanism of steroid transformations including purification of the enzymes involved and detailed examination of their molecular properties and catalytic mechanism. 2. The substrate specificity of these enzymes, especially on a comparative basis, among microbial and mammalian enzymes. 3. The design of specific and selective inhibitors of these enzymatic reactions with a view to establishing the functional significance of these reactions. Particular efforts are to be devoted to the design of active-site-directed irreversible inhibitors with capacity to bind covalently to the enzymes. The evaluation of these inhibitors in purified steroid-metabolizing enzyme systems as well as in more highly organized systems will be undertaken, with the view to perturbing steroid hormone synthesis and the normal functioning of endocrine processes.